It is known that photographic images having extremely high contrast can be formed by using a certain kind of silver halide.
For example, a lith development system, i.e., a process of obtaining extreme contrast images by processing a lith type silver halide photographic material containing silver chlorobromide with a hydroquinone developer (lith developer) having a very low (lower than about 0.1 mol/liter) sulfite concentration is well known.
Also, a process of obtaining extremely high contrast negative photographic images by processing a surface latent image type silver halide photographic material containing a hydrazine derivative (e.g., the specific acylhydrazine compounds as described in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606, 4,311,781, etc.) with a solution having a high pH and containing a sulfurous acid preservative of at least 0.15 mol/liter (hereinafter, this process is referred to as a hydrazine contrast development system) is well known.
Furthermore, a process of obtaining extremely high contrast images by processing a photographic light-sensitive material containing a tetrazolium compound with a PQ type or MQ type developer containing a sulfite in a relatively high concentration together with a hydroquinone (Q) as a developing agent and an auxiliary developing agent such as a 1-phenyl-3-pyrazolidone (P) or a p-aminophenol (M) for obtaining super additivity is disclosed, for example, in Japanese Patent Application (OPI) Nos. 18317/77, 17719/78, and 17720/78 (hereinafter, this process is referred to as a tetrazolium contrast development system) (the term "OPI" as used herein means an "unexamined published patent application").
The lith development system, hydrazine contrast development system, and tetrazolium contrast development system described above all can give an extremely high contrast of a gamma (.gamma.) value of over 10 but, on the other hand, since the slope of the characteristic curve at the toe is very steep, these systems have the disadvantage that when the exposure amount is reduced, the images of fine lines are difficult to obtain. For example, when a letter original is photographed using a process camera, in the case of an extreme contrast light-sensitive material showing a very steep slope at the toe portion of the characteristic curve, the letter density is suddenly reduced with under exposure to make the images unreadable as letters. Accordingly, these systems have the disadvantage of narrowing the latitude as to deviation in exposure amount for a light-sensitive material having such a high contrast.
This disadvantage can be eliminated by using a light-sensitive material having a relatively soft tone of less than 10 in .gamma. value. That is, when the exposure amount is reduced in the case of a soft tone light-sensitive material, the sudden reduction of the density of letter images does not occur and also when the exposure amount is reduced in this case, the letter images formed have a density which can be used in the subsequent reversing step and thus images which can be used as letters can be obtained.
As described above, a soft tone light-sensitive material has the advantage that the latitude in the low exposure side is broad but, on the contrary, has the disadvantage that a high background density (Dmax) is not obtained. That is, the density of the portion (solid black on a negative film) corresponding to the white portion of an original becomes higher as the .gamma. value at the high density area of 1.5 or more in density of the characteristic curve increases and a soft tone light-sensitive material has the disadvantage that Dmax is low since the .gamma. value at the high density side is low. An original for camera-ready art in line image photographing is composed of an original having a high letter density, an original having a low letter density and a low contrast, an original of Ming style type (narrow line width) or Gothic type (bold line width), an original having a colored base, etc., and the optimum exposure amount differs for each of these different kinds of originals.
In the case of photographing the original for camera-ready art composed of a combination of these originals each having a different optimum exposure amount, the selection of the exposure condition is very difficult for a light-sensitive material having a narrow exposure latitude. As a result, it is sometimes impossible to photograph the whole portions of the original for camera-ready art with good reproducibility by one photographing and also sometimes each portion of the original must be separately photographed different exposure condition for each.
In other words, when the exposure amount is reduced for reproducing black fine lines of an original, the background density (corresponding to the solid black portion on a negative film and shown by Dmax) is reduced and the density of white fine lines of the original (white lines in the black background) is low and collapsed. Also, when, on the contrary, the exposure amount is increased, black fine lines are collapsed in the images formed. Accordingly, a photographic light-sensitive material having a broad exposure latitude in such line image photographing and providing a high background density (Dmax) has been desired.